The present invention relates generally to serially recorded magnetic tape storage. More particularly, the invention relates to a system for detecting whether a magnetic tape has been previously recorded and, if so, in what format.
Digital computers have traditionally used some form of mass data storage to complement the main system memory. In today's computers main system memory is usually implemented using solid-state random access memory devices or RAM. Conventionally today's computer systems also employ a magnetic hard disk system as the primary mass storage medium.
Although in the broadest sense, solid-state RAM and magnetic disk storage systems are both digital data storage media capable of functioning as computer "memory," the solid-state RAM is accessed far more quickly than magnetic disk. Thus, solid-state RAM is usually relegated to time critical data storage needs. In contrast, disk storage has a slower access time but is less costly on a per byte storage basis. In addition, unlike most solid-state RAM devices, which require essentially a continuous connection to a power source, magnetic disk storage is nonvolatile and is capable of storing data even when the power is turned off. Thus magnetic disk storage media is often relegated to the function of primary mass data storage, i.e., the place where executable computer code, data records, help files and the like are stored for use on a sporadic basis.
Although presently lower in cost than solid-state RAM storage, magnetic disk storage technology is still quite costly. Although prices vary depending on the storage capacity, the hard disk subsystem still comprises a major cost component of most business computers in use today. Overall, hard disk systems are quite reliable. However, head crashes and other hard disk system failures do occur from time to time. Failures of this nature can be quite catastrophic, since head crashes often cause physical damage and thus it is not possible to recover data after a head crash has occurred.
To guard against data loss due to hard disk failure many computer systems employ a secondary mass storage system as a backup. Magnetic tape storage is by far the preferred medium for secondary storage today. Magnetic tape has the advantage of being far more economical than even magnetic disk technology on a per byte storage basis. Of course, because the data must be stored serially (i.e. longitudinally) on the tape, data access time is slower than with disk.
No doubt in part due to its cost advantage, magnetic tape media, sometimes called "streaming tape" media, has proliferated as the means for providing backup of computer systems and computer networks. This rise in popularity has given rise to a proliferation of different tape formats, each offering certain advantages to different segments of the marketplace. Today streaming tape is usually sold in a self-contained cassette or cartridge, of which there are a number of different types. Unfortunately, the proliferation of different data storage formats and different cartridge types are incompatible with one another. Thus it has not been traditionally possible for the user of one system to exchange data with the user of a different system. Similarly, this incompatibility has presented problems for users who are upgrading to new equipment but who may have important data stored on an old-style cartridge or in an incompatible format.
The way around this problem for most users has been to employ two separate tape drive systems in order to effect a data transfer or migration from one format to the other. This, of course, requires the user to own or have access to both types of equipment. It would be far more convenient if the user could acquire a single tape drive which is automatically capable of determining or identifying the format of a given tape and automatically adjusting the operating parameters to allow that tape to be read, and preferably written in the tape's native format. Unfortunately, present-day tape drive systems have not been capable of this.
The present invention addresses the tape incompatibility problem by providing a system which will automatically identify the format of a data storage tape. Once the format is identified, the drive parameters may be adjusted appropriately to allow the tape to be read, and optionally written in either the tape's native format or in a new format. The invention thus renders the tape drive system far more versatile and easier for the less technically skilled user to operate.
The invention provides a method of identifying the format of a data storage tape in which the tape and tape head are moved in a preprogrammed manner to perform a series of investigative steps designed to efficiently and quickly gather data about which the format and cartridge type of the tape can be deduced.
More specifically, as part of the series of investigative steps, the tape is moved longitudinally while searching for physical format or cartridge type holes and a datum indicative of the cartridge type is stored. In addition, a head location datum is at least temporarily stored to indicate the longitudinal position of the transducer head relative to the tape.
Also during the investigative steps, while the tape is moved longitudinally, the transducer head is moved laterally, searching for laterally spaced magnetic marks or fingerprints. If laterally spaced magnetic marks are located, a lateral spacing datum is at least temporarily stored.
In addition, during the investigative steps, while the tape is moving longitudinally, a search is performed for longitudinally spaced magnetic marks or fingerprints. If longitudinally spaced magnetic marks are located, a longitudinal spacing datum is at least temporarily stored. Then, using the head location datum, the physical format datum and at least one of the stored lateral spacing datum and stored longitudinal spacing datum are used to identify the data format and physical cartridge type of the data storage tape.
The above described method is can be implemented to permit a backward looking mechanism, i.e., the method may be performed while the tape is being moved in reverse to the beginning of tape position. The above method steps are preferably integrated, allowing the cartridge type and recording format information to be gathered simultaneously. This results in an efficient format identification system.